9709 P33 - Jun 2018 - Q10
2143
The points A and B have position vectors \(2\mathbf{i} + \mathbf{j} + 3\mathbf{k}\) and \(4\mathbf{i} + \mathbf{j} + \mathbf{k}\) respectively. The line l has equation \(\mathbf{r} = 4\mathbf{i} + 6\mathbf{j} + \mu(\mathbf{i} + 2\mathbf{j} - 2\mathbf{k})\).
(i) Show that l does not intersect the line passing through A and B.
The point P, with parameter t, lies on l and is such that angle PAB is equal to 120°.
(ii) Show that \(3t^2 + 8t + 4 = 0\). Hence find the position vector of P.
